var kvArray = [{key: 1, value: 10},
  {key: 2, value: 20},
  {key: 3, value: 30}];

var reformattedArray = kvArray.map(function(obj) {
  var rObj = {};
  rObj[obj.key] = obj.value;
  return rObj;
  })
console.log(reformattedArray)